I get why you're sad that you don't have photos of your Mum outside of that period, but I don't really get why you think that that means she didn't think the rest of her life was worth documenting?
Your Mum's photo taking habits sound a lot like mine. I take photos because they're of something I want to remember.
I've got loads of photos of DD that I took, or photos of DD with DP, or with her grandparents etc, or group shots that include me that I took with a timer, because those are things I'm interested in seeing again. And there's loads of photos of me with DD and other family members that for instance DP took.
But when I'm off doing something by myself, I don't need photos of me. I'm taking photos of the things I saw, the experiences I had. When I had those experiences, I couldn't see me, so why would I want the photos of them to include me?
Earlier this year I did a big trip by myself, cycled around 400 miles over a week. I took around 100 photos. Of the view, of people I met, of hotel rooms, of pints of beer in pub gardens, of my bike laden with all my luggage, of the flat tire I got etc. There's a grand total of two pictures of me during that trip, one that DP took out of our bedroom window as I left, and one of me at the finish line with the Cutty Sark in the background, that I took to send on Whatsapp to other people. That photo wasn't really for me. I wanted the pictures I took on that trip to be a reminder what what I saw, to tell a story so that I could remind myself "Oh yes, thats where I was on that day, that's where I got a flat tire, that was the absolute shithole I stayed in on night 3"
Don't get me wrong, I'm not averse to my own image. Yes, I'm a balding fat 40 year old man, but I have absolutely no body image issues. In fact I have a belief that I'm an absolute physical specimen that goes entirely unsupported by reality.
I think it may partly be that I'm aphantasic. I can't form pictures in my mind. So 30 seconds after I've seen a lovely view, I couldn't describe it to you. So for me, pictures are way to remember what I can't remember. They're a way of saying "This is what I saw through my own eyes". I don't want a selfie, that's not useful to me, it's not what I saw.
Sorry, that was long winded, but what I'm trying to say is that I don't think you can say that a lack of pictures of your mother means that she didn't find her experiences outside of being a mother worthy of documenting. It's not like she didn't take any photos during that time. She just took the photos that meant something to her, rather than the ones that other people would want to see.